This invention relates to the field of networking. It is more particularly directed to seamless networking support to devices connected via a serial communication.
The majority of handheld computing devices, such as palmtop computers, consumer electronic devices, pagers, cell phones, and digital cameras are equipped with serial port communication interfaces. Such devices are connected to other computer systems using a RS-232 serial cables or modem connected telephone lines. Point-to-point protocol (PPP) is the most commonly used protocol for connecting serial port devices to wired networks such as the Internet. Since-users of handheld devices are mobile, it is desirable to enable wireless connectivity over serial links and provide seamless mobile and non-mobile networking solution to users of portable computers.
Having a wireless link enables mobility and ease of use. Wireless connectivity together with mobility enables a rich set of new applications such as seamless data synchronization, continuous access to network resources, collaboration among a group of people, etc. For indoor wireless access, several short range wireless technologies are being developed by various industry groups. Due to power, cost, and regulatory constraints, it is expected that the range of the wireless link from a palmtop device to a static access point is quite short (10 m-20 m). Hence, a set of access points are installed to cover a usage area such as an office building. Such a solution implies that the wireless access and mobility will be limited to a range covered by these access points, but this is generally not a very significant limitation considering that these palmtop devices will be mostly used inside closed areas, such as office buildings, airports, shopping centers, hotel rooms, homes, etc.
FIG. 1 shows an example of a Intranet 110 providing wireless access to handheld devices 130, 132, 135. Each access point 120, 125 acts as a bridge between the wireless and wired medium. A handheld device 130 within the communication range 140 of the access point 120 can access the network through that access point 120. This scenario of a system that supports wireless access using short-range radio anywhere inside a building covered by access points highlights the problem of how to provide mobility support for these devices 130, 132.
The support should allow these devices to seamlessly move from the range of an access point range 140 to another access point range 150. This should still preserve the network connectivity-without the users being aware of the hand-offs from range to range. It would be advantageous to have-a way which provides a seamless, secure mobility protocol for this kind of scenario.
Serial links provide synchronous or asynchronous byte or bit oriented communication which do not have notion of packet boundaries. However, network layer protocols, such as IP, require an underlying link layer that is packet oriented. The Point-to-Point Protocol (PPP), RFC 1661, Internet Engineering Task Force Standard is herein incorporated by reference in entirety. The PPP protocol provides such a packet oriented link layer interface to the network layer, hence a large number of devices that use serial communication run PPP protocol to connect to the Internet.
PPP protocol provides a standard method for transporting multi-protocol network (IP, IPX, AppleTalk . . . ) datagrams over point-to-point links. It is comprised of mainly three main components: 1) A method of encapsulating multi-protocol datagrams; 2) A Link Control Protocol (LCP) for establishing, configuring, and testing data-link connections; 3) A family of Network Control Protocols (NCPs) for establishing and configuring different network layer protocols. PPP is connection oriented. The peers establish a PPP connection before communicating any data. Connection establishment include negotiation of a set of parameters for LCP, NCP, and other control protocols (Encryption Control Protocol (ECP), Compression Control Protocol (CCP), etc.). After this network layer datagrams can be sent over the link.
PPP protocol is used between two PPP peers located at the end of a PPP link: user (device) side PPP peer and network side PPP peer. The network layer above the network side PPP peer is the gateway to the Internet and forwards IP datagrams between a mobile device and the Internet over the PPP link. The network layer above the device side PPP peer enables legacy applications to be run transparently over the PPP links.
Mobile IP provides a link layer independent mobility solution for mobile hosts connected to the Internet. It can be used for various kinds of link layers: PPP links, Ethernet links, ATM etc.
A mobile host has a permanent home IP address which does not change upon movement to a new subnet. When a mobile host moves to a new subnet other than its home subnet, it registers its current locationxe2x80x94the IP address of a foreign agent in the new subnet or a temporary IP address obtained by mechanisms such as DHCP- with an agent in its home subnet, called home agent. The home agent then intercepts IP packets destined to the mobile device and forwards them to the current location by mechanisms called IP-IP encapsulation and IP tunneling. If the mobile host has registered the IP address of a foreign agent with the home agent, then the packets are forwarded to this foreign agent which then forwards them to the mobile host. If the mobile host has registered a co-located IP address with its home agent, then the packets are directly forwarded to the mobile host. For security reasons, a mobile host authenticates itself to its home agent with each registration. The authentication is based on a shared secret key that can be manually configured in a mobile device and its home agent.
A first attempt to provide a seamless mobility solution for palmtop devices might be to use Mobile IP which is an already established standard. FIG. 2 shows such a scenario. A mobile host device MH 250 establishes a PPP connection 230 with the access point AP1220 which is a gateway to the Internet xe2x80x98Internetworkxe2x80x99 215. AP1220 also runs a Mobile IP foreign agent, FA 225. All packets destined for the mobile host 250 will be first routed to the home agent HA 210. HA 210 then forwards the packets to the foreign agent FA located in AP1220. FA 220 then forwards these packets to the mobile device MH 250 over the PPP link 230.
When the mobile device 250 moves out of range of AP1220 to the range of AP2225, it has to establish a new PPP connection 240 with AP2225. If AP1220 and AP2225 are not in the same subnet, it also has to register its current locationxe2x80x94IP address of the current foreign agentxe2x80x94with its home agent 210 using the Mobile IP registration and authentication protocol. After this the communication to the mobile device can resume. Since the range of the wireless link is short, these operations may need to be repeated quite frequently (with each hand-off to a new access point).
Such a solution has the following drawbacks:
A new PPP connection needs to be established with every hand-off. PPP connection establishment includes link configuration, authentication, network layer configuration, and optional encryption and compression parameter negotiations. Each parameter negotiation phase increases hand-off latency which may be unacceptable in micro-cellular, indoor wireless environments. Additionally, these negotiations waste bandwidth by introducing extra traffic on the wireless link.
Layering Mobile IP on top of PPP adds to handoff latency because Mobile IP layer performs its own set of registration and authentication exchanges;.
This solution is difficult to deploy since Mobile IP protocol is not supported on most mobile devices.
In order to overcome the problems identified, the present invention provides a method, apparatus and/or protocol for emulating a direct serial line over a multihop packet data network. Use of the serial line emulation protocol of the present invention allows devices equipped with serial communication interfaces to be connected over a packet data network to their peers.
Another aspect of the invention provides support for mobility without requiring changes to the networking software on mobile and non-mobile devices. Network connectivity for devices is preserved after handoff from one access point to another access point.
In an embodiment, the invention is used to emulate a direct RS-232 cable connection between a mobile device and its peer through a wireless access point. When the mobile host moves, the cable emulation protocol reestablishes the emulated RS-232 link, thereby hiding effects due to mobility from the higher layers.
In another embodiment, the present invention establishes a persistent PPP connection between a mobile device and a PPP server. Instead of running a PPP server on each wireless access point, the PPP function is aggregated into a server located in the network. The access point acts like a PPP proxy, bridging the wireless and the wired medium. On the wireless side the access point emulates an RS-232 lines, while on the wireline side the access point emulates a byte stream tunnel to the PPP server. When a portable device moves, it notifies its PPP peer using a new PPP option to switch the byte stream tunnel to another access point. Since the portable device carries its PPP state with it, it always remains connected to the same PPP server as before (albeit over a different emulated wire). No change in IP address is required and, consequently, none of the active connections are disrupted.
Another aspect of the proposed invention is that negotiation phases of higher layer protocols are avoided. Still another aspect of the present invention provides security by making PPP protocol mobility aware and thereby requiring authentication checks before moving a PPP tunnel end-point. Unlike Mobile IP solution which is specific to the IP protocol, the present invention supports seamless mobility for all networking protocols, including IP.